Hi all im new to this Forum,but not to fish keeping. I have a 55g set up with a heavy fish load, and i do mean heavy it is a breeding tank for live bearers. i have bulbs coming to me for my fixture because right now my few plants are suffering, as i am at less than 1wpg. The fixture is 4x54 watt T5 HO.

Basically what i want to know is, if i put 4 bulbs in and run at 3.92WPG do i have to have co2?Or can you do a higher light low tech set it? I do not dose ferts due to my fish load. As i said it has a very heavy fish load most of the time, because even when i do sell off my fry there seems to be replacements born almost instantly.

CO2 is mandatory at those lighting levels!!!!

stick with only 2 bulbs w/o CO2

You'll end up with loads of algae. 2wpg is pretty much the limit for a non-co2/fert tank.

Even 2 watts per gallon on that size tank, with T5 bulbs, is likely to be a problem when you don't have CO2 and enough fertilizing to keep the plants growing at the speed the lights are driving them to grow. If you raise the fixture a few inches above the tank, run only two bulbs, and limit the photoperiod to 8 hours a day or less, you stand a chance of it working.

not that this prolly makes much difference but it is on mounting legs setting about 3 inches above the tank and about 6 to 8 inches above the water level.

Algae isnt always a bad thing it will feed my monster placo lol

A 55 gallon tank is about 21 inches tall, so with 3 inches of substrate, the substrate is about 18 inches below the top of the tank. A typical light fixture sitting on top of the tank would have the bulb about 2 inches above the top of the tank (wild guess). So, with the 3 inch legs you have, the light bulbs should be about 23 inches above the substrate. That means the light intensity at the substrate with the legs is about 20/23 times what it would be with a "standard" setup, or about 87% or less, but not less than 75%. An average of 87 and 75% is about 80%, so 2 watts per gallon with your light would be about 1.6 watts per gallon when raised that much. But, T5 fixtures give at least 1.3 times as much intensity than AH Supply type fixtures, so that 1.6 watts per gallon becomes about 2.1 watts per gallon.

All that says is that raising it 3 inches is probably not enough. I would try suspending it and raising it about 6 inches or a bit more. Remember, this is with only two bulbs, not 4. None of those numbers can be assumed to be acccurate, just a crude way to guess at how high the light fixture needs to be.

Ok well at least i understood most of that, so run 2 bulbs and keep the rest as spares got ya.

The trade offs for each light level conflicts.

You want low tech, eg no CO2 because you want less work, this also means less light which drives CO2 demand.

The light and the CO2 are dependent, so the idea is a confliction of trade off goals.

Regards,
Tom Barr

Is it possible for a high fish load to produce enough CO2 for moderate lighting say 2.5 to 3 Wpg? And the plants in turn produce enough O2 for the fish?

I plan to stay low tech so if it wont work no big deal. Also is it safe to do a "Noon Burst" say run 2WPG all the time and for a couple hours a day run 4 WPG?

Also what happens if you run High Light without CO2?

The tank has a fairly high fish load (at the moment, until some of my molly's are big enough to sell) i would guess (and its only a guess) 60 to 80 fish in a 55g, mostly very small fry, under 1/2 inch.

If i could afford a Pressurized CO2 unit i would get it in a heart beat, but right now its just not in the budget.